The invention relates to a device which is suitable for determining the surface moisture of, in particular, absorbent, fluid-absorbing or fluid-transporting two-dimensional structures such as, for example, filter paper, baby diapers, sanitary towels, incontinence diapers, patient underlays, nonwovens or textiles. In addition, in the case of materials of homogeneous moisture distribution, the surface measurement can provide information on the moisture content in the interior of a system.
For the assessment of materials of the type described above, it is frequently necessary to know the moisture conditions on the surface or in the interior of the system, above all when their use value is mainly determined by this parameter. This is the case, for example, with baby diapers, incontinence diapers, patient underlays and textiles which come into direct contact with the skin. In many cases, the moisture conditions at the surface are correlated with those in the overall system. However, this is not always the case, in particular if the structures to be examined are composed of several layers of different suction capacity and absorbency. Hygiene articles, medical underlays and towels may be mentioned as examples thereof. These are composed of a highly absorbent core and a covering layer of greatly reduced fluid absorption, such as, for example a polypropylene nonwoven.
A large number of methods and devices for the measurement of moisture are known. Thus, these can be determined on the object, for example via changes in conductivity, inductivity, capacitance or the intensity of IR radiation. Frequently, however, these methods have the feature that they cover not only the surface conditions of the system but also deeper layers. By contrast, using the measuring apparatus described in accordance with the invention, it is possible to determine the moisture conditions on the surface and hence to detect the surface moisture, for example in the case of contact with the skin, in a manner which is substantially closer to practice than in other methods.